Optical frequency-domain reflectometry (OFDR) is technique through which a swept-wavelength laser source is used to discriminate between different locations along the length of an optical fiber. OFDR measurements can be used in applications including sensing distributed temperature and/or strain in optical fibers and determining the location of bends, reflections, and faults in fiber optic networks with high spatial resolution. Being a form of swept-wavelength interferometry, OFDR also provides a spectral characterization of each reflector or scattering location in the fiber (in addition to positional information) from which a variety of distributed fiber optic sensing techniques based on OFDR have been developed. Distributed OFDR measurements can be performed with several optical fiber scattering types such as using multiple discrete or continuous fiber Bragg gratings (FBGs) or the intrinsic pattern of Rayleigh scatter in the optical fiber to measure temperature, strain, shape and position, and other physical phenomena.
Optical dispersion, often referred to as Group velocity dispersion (GVD), exists to some degree in all optical waveguides and causes degradation in the coherence of the OFDR signal. Optical dispersion causes a smearing of the amplitude response of the fiber making it difficult to distinguish reflective events in an OFDR measurement. Further, optical dispersion prevents distributed sensing applications from being able to properly match a location in a measurement scan, (which corresponds to a delay along the length of a measurement), to the same location in a baseline measurement of the fiber. In distributed sensing applications, misalignment between an OFDR measurement scan and an OFDR baseline scan is known as differential delay. A differential delay signal can be used to make highly accurate distributed strain measurements by compensating for elongation of an optical sensor in a strained measurement. However, optical dispersion distorts this measurement of differential delay, particularly at longer sensing lengths, and causes inaccuracy or prevents distributed measurements. This reduction in OFDR measurement data quality undermines the reliability and accuracy of OFDR-based distributed sensing.